Pulse radar method, pulse radar sensor and corresponding system

ABSTRACT

In a pulse-radar method, in particular for motor vehicles, different time slots ( 21, . . . , 24 ) of a time frame ( 20 ) are predefined. During one time slot, a radar sensor ( 1 ) emits at least one radar pulse and receives the echo signal(s). During the remaining time slots ( 22, 23, 24 ) the radar sensor ( 1 ) monitors whether interference signals occur. On the basis of the interference signals occurring per time slot ( 21, . . . , 24 ), a decision is made whether the radar sensor ( 1 ) should continue its transmitting and receiving operation in the predefined time slot ( 21 ) or should switch to one of the remaining time slots ( 22, 23, 24 ) of the time frame ( 20 ). The method is suited for the concurrent operation of a plurality of radar sensors, without this causing interference.

BACKGROUND INFORMATION

[0001] The present invention is directed to a pulse-radar method, inparticular for motor vehicles, in which occurring interference signalsare monitored.

[0002] From DE 196 31 590 A1, a radar system is known that worksaccording to such a method. In the FMCW-radar method employed there,individual time periods are defined in which the oscillator emitsmodulated high-frequency signals. During at least one time period, nosignals used for measuring radar targets are emitted. The interferencesignals occurring there are recorded and evaluated, together withrecorded radar signals, so as to be able to classify them as possiblewrong targets.

SUMMARY OF THE INVENTION

[0003] Using the measures of the claims, it is possible to avoid, or atleast reduce, mutual interference of pulse-radar systems (short-rangeradar SRR), in particular when their detection ranges overlap and/or aredirected toward each other. This is decisive mainly in the case ofsurroundings sensor systems of motor vehicles where substantiallyidentical sensors emit radiation towards each other. This happensespecially in systems such as park pilot systems (PPS) and dead-angledetection (DAD), since in these cases the detection ranges of the radarsensors may be directed toward each other when motor vehicles approachor pass each other. The cause of this interference is the high bandwidthof the SRR radar pulses. This broadband width is basically required inorder to ensure a high-sensitivity resolution of the radar sensors.Essential for the present invention is the prevention of mutualinterference in the pulse radar by operating the individual radarsensors in time-staggered time slots of a time frame. For this purpose,two measuring functions of a radar sensor are defined. During onepredefined time slot, a radar sensor emits at least one radar pulse andreceives the echo signal(s). This measuring function is used for theactual obstacle detection. The second measuring function is used todetect interference, i.e., during the remaining time slots of the timeframe, the radar sensor monitors the electromagnetic surrounding field.On the basis of the interference signals occurring per time slot, it ismonitored whether a respective time slot is free of interference. Then adecision is made whether the radar sensor should continue itstransmitting and receiving operation in this time slot or should switchto one of the remaining time slots of the time frame.

[0004] These measures make the pulse-radar method (SRR) effectivelyusable in short-range sensing in the first place, in particular for PPSand DAD. Without applying the measures according to the presentinvention, mutual interference would occur continually once a certainequipment level of motor vehicles had been reached.

[0005] The additional effort of the present invention when compared toconventional systems only consists in a diverging control of alreadyexisting components on the basis of evaluated signals. Therefore, themeasures according to the present invention may easily be retrofitted inalready existing systems, for instance by changing the software.

[0006] Due to the time restriction of the radar sensor emission, theaverage interference emission is reduced, thereby lessening theelectromagnetic environmental impact.

[0007] An averaging of measured values, such as required, for instance,in a pseudo-randomized encoding of trigger pulses and necessitatingcorresponding additional expense, may be dispensed with.

[0008] According to Claim 2, in order to decide whether interference isoccurring in a predefined time slot, it is advantageous to consider thenumber of pulses currently occurring in this time slot as well as theirfluctuations.

[0009] For the decision whether interference is occurring in at leastone of the remaining time slots, it is advantageous, according to Claim3, to take the instantaneous amplitude values in the particular timeslot into account and to determine whether they exceed a predefinedthreshold.

[0010] After finding a time slot having little or no interference, it isadvantageous, according to Claim 4, if the radar sensor begins itstransmitting and receiving operation in the next time frame, in theparticular time slot that occupies the same time position within thetime frame.

[0011] According to Claim 5, it is advantageous if radar sensors thatare at risk for mutual interference, agree to a uniform time frame withcorresponding time-slot division.

[0012] The measures of Claims 4 and 5 contribute to making it possiblefor a plurality of radar sensors to operate next to each other withoutinterference.

[0013] It is advantageous if, according to Claim 6, a radar sensor and,if appropriate, additional radar sensors, discard(s) its (their)measurements if interference occurs in the particular time slot(s) usedin each case for the transmitting and receiving operation. This resultsin reliable measurements.

[0014] According to Claim 7, radar sensors search for time slots havinglittle or no interference according to the random principle and keep onusing such time slots until interference occurs there.

[0015] According to Claim 8, radar sensors belonging to a common systemor motor vehicle, in particular when arranged in close proximity, areadvantageously precontrolled in such a way that they occupy differenttime slots within the time frame. A painstaking search for time slotswithout interference will then be unnecessary.

[0016] If heavy external interference occurs in such radar sensors,according to Claim 9, they reroute only temporarily to time slots havingless or no interference and resume their precontrolled operation oncethe external interference has lessened.

[0017] According to Claim 10, it is advantageous that a differentpolarization is used for reducing interference of simultaneously activeradar sensors.

[0018] Claim 11 shows an advantageous refinement of a pulse-radarsensor, in particular for implementing the method according to thepresent invention, by which a simple switching of a time slot ispossible for emitting or receiving the radar pulses. This requires onlya redirecting as a function of an evaluated signal.

[0019] Claim 12 indicates how radar pulses may be evaluated forinterference in a simple manner.

[0020] According to Claim 13, interference in the remaining time slotsmay be detected by simple means.

[0021] Claims 14 through 16 indicate measures that effectively reducemutual interference of radar sensors. In particular, the simultaneoususe of different time slots for different radar sensors and the use ofdifferent polarizations results in substantial interference immunitywithin a system.

BRIEF DESCRIPTION OF THE DRAWING

[0022] Exemplary embodiments of the present invention are explained ingreater detail on the basis of the drawings.

[0023] The figures show:

[0024]FIG. 1 a basic construction of a radar sensor for implementing themethod according to the present invention;

[0025]FIG. 2 the staggered utilization of time slots by different radarsensors; and

[0026]FIG. 3 the mutual interference influencing by radar sensors of twomotor vehicles.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0027] As shown in FIG. 1, a microwave-carrier oscillator 2 in radarsensor 1 generates a carrier frequency. With the aid oftrigger-pulse-controlled fast switches 3 and 4, in particular diodeswitches, oscillation packets are formed from the continuous signal ofcarrier oscillator 2. Via an antenna 5, the oscillation packet formedvia switch 3 is emitted. After reflection at a possible obstacle, partsof this signal are picked up by receiving antenna 6 and conveyed to amixer 7. This mixer 7 mixes the oscillation packet formed via switch 4with the incoming signal. Mixer 7 provides an output signal 8 if thereceived and the sampling signal (via switch 4) coincide in time. Withthe aid of a controllable pulse delay 9, the sampling pulse is delayedwith respect to the transmission pulse, due to the fact that triggerpulse 11 for switch 4 is conveyed via pulse delay 9, whereas triggerpulse 10 reaches switch 3 without a delay. The control of pulse delay 9is implemented by a control voltage 14. The magnitude of the delay isdetermined by the known correlation of both variables. Output signal 8of mixer 7 is forwarded to a control unit 13 via a band-pass amplifier12. Control unit 13 evaluates this echo signal.

[0028] The delay time at which mixer 7 provides an output signal (echosignal) is then equal to the runtime of the waves between radar sensor 1and the obstacle. The distance from the obstacle is determined from theknown propagation speed of the electromagnetic waves and the measuredtime.

[0029] Control unit 13, which may be a microprocessor, provides triggerpulses 18, which, after appropriate conditioning, are conveyed toswitches 3 and 4 as their trigger signals 10 and 11, respectively. Onthe one hand, trigger pulses 18 are conveyed to switch 3 via a pulsegate 15 and a pulse shaper 16 and, on the other hand, to switch 4 viapulse delay 9 and pulse shaper 17.

[0030] To transmit the oscillation packets, i.e., the radar pulses, atime frame 20 is predefined according to FIG. 2, which in the exemplaryembodiment shown is divided into time slots 21, 22, 23, 24. After firsttime frame 20 has elapsed, another time frame begins again with timeslot 21. Time frame 20 specifies the cycle time of the measurements. Themeasuring phase, i.e., the time during which a radar sensor emits radarpulses and evaluates their echoes, corresponds to one of these timeslots, such as time slot 21. The monitoring phase, i.e., the time of theremaining time slots 22, 23, 24 within time frame 20, is used to monitorinterference, which is caused in particular by other radar sensors. Suchmonitoring allows one or a plurality of other radar sensors to conducttheir measurements without interference. In FIG. 2, one measuring phase(time slot) and three monitoring phases (remaining time slots) wereassumed for each radar sensor by way of example. In this way, fourdifferent radar sensors 401, 402 and 411 and 412 may be operated in aninterference-free manner. Their measuring phases, as indicated in FIG.2, occupy different time slots 21, . . . , 24. Of course, any number ofwhole-number ratios of monitoring and measuring phases is possible. Thissubdivision, for one, is restricted by a lower limit for the measuringrate, i.e., the shortening of the measuring rate must technically stillbe tolerable so as to provide reliable results, and, for the other, isrestricted by the length of a time frame, i.e., the repetition ofmeasurements must be adapted to the requirements (the higher thepossible absolute speed of a motor vehicle, and the higher the relativespeed variation, the shorter a time frame 20 must be).

[0031] The setpoint selection of time frame 20 and of time slots 21, . .. , 24 is specified by control unit 13 by the repeat frequency oftrigger pulses 18, and/or by pulse gate 15. Using pulse gate 15, whichis realized by an AND-circuit, for example, to which the control unitconveys gate signals 19 in addition to trigger pulses 18, the triggerpulses may be transmitted further or suppressed and the measuring phasethereby switched off or on—suppression or emission of the radar pulses.Pulse gate 15 may also be an integral component of control unit 13, orbe realized within the microprocessor by internal signal linkage. Eachradar sensor is designed such that interference is able to be detected.For this purpose, the sampling function of the radar sensor is inoperation at all times (triggering of switch 9 in all time slots).

[0032] If a plurality of radar sensors cooperate in one system, it ispossible to transmit an interface signal 30 to control unit 13 in orderto ensure that the radar sensors of this system all have their measuringphases in different time slots and do not interfere with each other.

[0033] The interference by other radar sensors manifests itself bypulses whose distribution in time is random.

[0034] In the monitoring phase, mixer output signal 8 is monitored withrespect to amplitudes that exceed a certain threshold. If these happenat a certain occurrence rate, it is assumed that another radar sensor istransmitting in this phase. The monitoring radar sensor will then avoidthis range as measuring phase.

[0035] In the measuring phase, echo and interference pulses occursimultaneously. If the number of pulses is approximately constant, itmay be assumed that no interference signals are present. If the numberof pulses fluctuates and is high, then it is highly likely thatinterference pulses are present. The measurement must then be discardedand restarted after an agreed-upon interval.

[0036] It is advantageous if all pulse-radar systems observe a uniformmeasuring cycle. If the interference signal is detected in a measuringcycle and if the interference regions are determined, then it can bepredicted which time slots must not be used by the involved radarsensors. The monitoring radar sensor may synchronize to a vacant timeslot in the next measuring cycle, such as time slot 21, and retain thisslot during the further measurements.

[0037] If two or a plurality of radar sensors are transmittingsimultaneously and the interference is such that at least one radarsensor encounters interference, the measurement is discarded. Thisrequires a threshold-decision element for ascertaining whetherinterference is present in the remaining time slots of the time frame.If a plurality of radar sensors encounters interference, the measurementis discarded in both radar sensors.

[0038] Through monitoring, the radar sensors will ascertain free timeslots once again. In order to avoid that the next free time slot is usedagain by a plurality of radar sensors, the sensors begin transmitting ina free time slot according to the random principle.

[0039] Since it cannot be excluded with the complete certainty under therandom principle that a plurality of radar sensors is transmittingnevertheless, the current measurement is discarded in the event of newinterference and a free time slot is searched for again on the basis ofthe mentioned principle.

[0040] The control of the measuring and monitoring function of the radarsensors may be carried out in a central control device or in the radarsensor itself. In the latter case, a processor (control device 13) inthe radar sensor is required for this purpose.

[0041] In order to minimize the interference in the radar sensors in amotor vehicle from the outset, adjacently located sensors may betriggered (precontrolled) by a common control device in such a way thatthey use different time slots. Control device 13 of the radar sensors isable to be appropriately controlled by this common control device viainterface signal 30. Only in the event of heavy external interferencewill they automatically deviate to time slots having less interference.After the interference has disappeared, the radar sensors reoccupy theiroriginal time slots. The change is possible because the mutualinterference of adjacently located radar sensors in a safety bumper, forinstance, is less than interference coming from radar sensors in anothervehicle whose radar sensors are pointing directly at each other, cf.FIG. 3.

[0042] In various radar sensors that are at risk for interference, it isadvantageous to use antennas having differing polarization, inparticular antennas having 45° polarization, for mutual decoupling. Inthis method, it is presupposed that no effective polarization rotationoccurs by the installation of the sensors behind the safety bumpers orother moldings. The rotation of the polarization would reduce thesuppression again. The simultaneous application of the time-slot methodand of the 45° polarization results in a very high interference immunityof the system.

[0043]FIG. 3 schematically shows the interference influence in twovehicles 40 and 41 each having two sensors 401 and 402 and 411 and 412,respectively.

[0044] So that substantially identical products from other manufacturersare compatible with the method according to the present invention, it isadvantageous when all radar sensors for which the likelihood of mutualinterference is very high use the same time frame 20 with the sametime-slot division.

What is claimed is:
 1. A pulse-radar method, in particular for motorvehicles, including the following steps: during a predefined time slot(21) of a time frame (20), a radar sensor (1) emits at least one radarpulse and receives the echo signal(s); during the remaining time slots(22, 23, 24) of the time frame (20), the radar sensor (1) monitorswhether interference signals occur; on the basis of the occurringinterference signals per time slot (21, . . . , 24), a decision is madewhether the radar sensor (1) should continue its transmitting andreceiving operation in the predefined time slot (21) or should switch toone of the remaining time slots (22, 23, 24) of the time frame (20). 2.The method as recited in claim 1, wherein, for the decision whetherinterference occurs in a predefined time slot (21, . . . , 24), thenumber of the instantaneously occurring pulses in this time slot (21, .. . , 24) and their fluctuations are taken into account.
 3. The methodas recited in claim 1 or 2, wherein, for the decision whetherinterference occurs in at least one of the remaining time slots (22, 23,24) of the time frame (20), the instantaneous amplitude values in theparticular time slot that exceed a predefined threshold are taken intoaccount.
 4. The method as recited in one of claims 1 through 3, wherein,after finding a time slot (21, . . . , 24) having little or nointerference, the radar sensor (1) begins its transmitting and receivingoperation in the next time frame (20) in the particular time slot (21)that has the same time position within the time frame (20).
 5. Themethod as recited in one of claims 1 through 4, wherein the radarsensors (401, 402, 411, 412) that are at risk of causing mutualinterference agree to a uniform time frame (20) with correspondingtime-slot division.
 6. The method as recited in one of claims 1 through5, wherein the radar sensor (1, 401) and, if appropriate, further radarsensors (402, 411, 412) discard(s) its (their) measurements ifinterference occurs in the particular time slot(s) (21, . . . , 24) usedfor a transmitting and receiving operation.
 7. The method as recited inclaim 6, wherein the radar sensor (1, 401) and/or the additional radarsensors (402, 411, 412) search for time slots having little or nointerference according to the random principle, and retain found timeslots having little or no interference until interference occurs there.8. The method as recited in one of claims 1 through 7, wherein radarsensors (1, 401, 402, 411, 412) belonging to a common system or a motorvehicle and, in particular, are arranged adjacent to each other, arealready precontrolled with respect to their time slots for thetransmitting and receiving operation in such a way that they occupydifferent time slots (21, . . . , 24) within a time frame (20).
 9. Themethod as recited in claim 8, wherein already precontrolled radarsensors reroute only temporarily, in particular in the event of heavyexternal interference, to time slots (21, . . . , 24) having little orno interference and resume their precontrolled operation once theexternal interference has lessened.
 10. The method as recited in one ofclaims 1 through 9, wherein, for radar sensors that are at risk formutual interference, a different polarization is used, for example apolarization that differs by
 450. 11. A pulse-radar sensor, inparticular for motor vehicles, having the following features: means (12)for generating a carrier-frequency signal; means (3, 4) for derivingradar pulses from this carrier-frequency signal; means for emitting (5)and receiving (6) radar pulses; means (13, 15) for the setpointselection of time slots (21, . . . , 24) within a time frame (20) forthe emitting and receiving of the radar pulses; means for evaluating(12, 13) transmitted radar pulses for occurring interference; means (12,13, 15) for changing a time slot (21, . . . , 24) for the transmittingand receiving of the radar pulses as a function of at least one signal(19), which is able to be emitted by the means for evaluating (12, 13,15) transmitted radar pulses.
 12. The pulse-radar sensor as recited inclaim 11, wherein the means (12, 13, 15) for evaluating transmittedradar pulses are designed such that a counting of the radar pulsesinstantaneously occurring in a time slot is possible and also arecording of their fluctuations.
 13. The pulse-radar sensor as recitedin claim 11 or 12, wherein a threshold-decision element is provided todetect whether interference is present in the remaining time slots (22,23, 24) of the time frame (20).
 14. A system comprising at least twopulse-radar sensors as recited in one of claims 11 through 13, whereinthe radar sensors (401, 402 and 411, 412) have a uniform time frame (20)and a common control device, in particular for adjacently arranged radarsensors, is provided for the precontrol of these radar sensors, in sucha way that each radar sensor is able to occupy a different time slotwithin the time frame (20).
 15. The system as recited in claim 14,wherein means (13, 15) are provided for deviating from this precontrol,in particular in the event of temporary, heavy external interference.16. The system as recited in claim 14 or 15, wherein the radar sensorshave different polarizations.